(1) Field of the Invention
The present invention concerns a device for identifying or authenticating a person by his print, as well as an identification or authentication method used by such an identification or authentication device. It finds an application in the field of biometric recognition and in particular in the field of identification or authentication by the analysis of finger or palm prints of a person.
(2) Description of Related Art
In biometrics, there are two processes:                identification, during which, from biometric information, the identity of a person is sought in a database; and        authentication, during which, from the claimed identity of a person and biometric data, identity is proved. The claimed identity can be obtained from a badge or a code.        
Biometric recognition is used for protecting installations, such as buildings or machines, or for obtaining the granting of rights, such as for example the issue of an identity card, payment of a pension, etc. This technology makes it possible to dispense with access codes or cards that may be stolen or falsified, or makes it possible to authenticate the bearer of these cards or the holder of codes. Use of this technology reinforces security since the probability that two persons have two identical biometrics is almost zero.
In the remainder of the description, the term “print” will apply both to a fingerprint and to a palm print.
In the prior art, a method of identifying a person from his print consists of:                a step of capturing an image of the print to be identified by at least one sensor,        a step of generating a template associated with the image captured by extraction of points of interest of the image, and        a step of verifying the identity of the individual.        
The step of verifying the identity of the individual consists for example of:                a step of searching, in a database of reference templates, for the reference template having the most similarities with said template associated with the captured image,        a step of measuring the resemblance between said template associated with the captured image and said reference template thus found, and        a step of taking a decision concerning the identity the person from the result of the measurement.        
In the prior art, a method of authenticating a person from a print thereof consists of:                a step of capturing an image of the print to be identified by at least one sensor,        a step of generating a template associated with the captured image by extracting points of interest of the image, and        a step of authenticating the person.        
The step of authenticating the person consists for example of:                a step of recovering the claimed identity of the person,        a step of seeking the reference template associated with the claimed identity thus recovered,        a step of measuring the resemblance between said template associated with the captured image and said reference template thus found, and        a step of taking a decision concerning the identity of the person from the result of the measurement.        
The step of seeking the reference template may consist of a recovery of the template recorded on a card, or of a template found in a database using a code.
In the context of a three-dimensional (3D) capture of the print, such an identification method is implemented by means of an identification device that comprises a plurality of sensors of the camera or CCD type, associated with a plurality of illumination means and processing means which, using images captured by the various sensors, implement the comparison step, the measuring step and the decision-taking step. An identification based on a 3D capture makes it possible to obtain better results than an identification based on a two-dimensional (2D) capture.
Such an identification device is disclosed in the document US-A-2006-120576. When the images are captured, the person wishing to be identified must keep his hand immobile in front of the sensor so that the captured images are sufficiently sharp to be usable. Such a sensor is said to be contactless.
Such an operating mode constitutes a disadvantage since it is often difficult for a person to keep his hands sufficiently immobile during the capture step.
In the context of a two-dimensional (2D) capture of the print, an identification device comprises a transparent rigid plate, illumination means, a sensor and processing means. The illumination means and the sensor are disposed behind the plate on which the person presses his finger. The image thus captured is then processed by the processing means. Use of such an identification device entails the squashing of the finger when it is in abutment on the rigid plate and consequently deformation of the print. Usually the systems retrieve a faithful image of the print only for the part of the finger (or respectively of the palm) in contact with the plate but, depending on the pressing force on the plate or other physical factors, the print may be deformed to a greater or lesser extent and the imaged surface, of greater or lesser size, giving rise to an uncertain identification. Such a capture is said to be contactless. In particular with the palm, it is impossible to make an acquisition of the entire surface comfortably while squashing the hand on a plate.
A three-dimensional capture of the print makes it possible to increase the analysis surface and therefore the number of items of information relating to the print while reducing the deformations compared with a two-dimensional capture with contact.